This invention relates to protective coatings for controlling the germination of seeds.
One of the most critical periods for plant emergence is the period between seed planting and germination. After planting, seeds usually must take in water before germination can start. This process is called imbibition. Most seeds initiate imbibition irrespective of the temperature of the soil. Once imbibition starts, however, germination must occur within a short period of time.
In contrast, ideal germination occurs only after the soil temperature increases to reach a critical soil temperature. If imbibition occurs long before the critical soil temperature is achieved, the seed can become diseased or die from chilling injury and crop yields are correspondingly lower. For example, dry seeds such as dry soy bean seeds typically contain about 7% to 14% by weight of moisture in their dormant state. If the seed imbibes substantial amounts of water above 14% at temperatures below the critical soil temperature, the seed is likely to suffer injury.
Thus, it is advantageous to control seed water uptake so that imbibition occurs only when the soil temperature is in the temperature range that promotes ideal germination for the end result that crop yields will be enhanced.
One of the inventors for the present invention, Ray F. Stewart, previously invented temperature-sensitive seed germination control as described in U.S. Pat. No. 5,129,180, which is incorporated herein by reference. In this invention, various types of coated organisms, such as coated seeds, were provided with a coating comprised of a polymeric material which has a temperature-dependent permeability. Preferred polymeric materials were side-chain crystallizable polymers. The polymer coating, when applied to a seed, prevents germination of the seed due to lack of water. The coating is permeable to water at a temperature above a transition temperature of the polymers for allowing germination of the seed.
A difficulty with the coatings described in U.S. Pat. No. 5,129,180 is that the coating systems are organic solvent based. There is concern that organic solvents can adversely affect the seeds, and any residual solvent left in the coatings can adversely affect plant growth and be deleterious to soil. Moreover, difficulties in the seed shedding the coating when temperatures are sufficiently high for seeds to germinate and grow have been noted, whereby the non-shed coating inhibits seed germination and plant growth.
Another problem noted with preexisting coatings is cracking at low temperatures due to the brittleness of the coating. Under these circumstances, water can prematurely be imbibed by the coated seed, resulting in premature germination and resultant stunted growth or death of the plant.
Accordingly, there is a need for a coating system for seeds and other organisms that is substantially solvent-free, and the formed coating does not crack at low temperatures and the coating is easily shed by the seed at temperatures conducive to ideal germination and growth.